Modern personal computers (PC) have been the beneficiary of much technological innovation over the past decades. Performance gains have been achieved by increasing processor speed, as well as increasing data transfer speed over input-output (I/O) busses. The progress in I/O speeds has largely come about through the implementation of new interface standards, although backwards compatibility has required that many legacy interfaces still be included on PCs.
In the x86 processor world, the original standard I/O interfaces include serial and parallel ports for external peripherals, the Industry Standard Architecture (ISA) bus for plug-in cards, and the Integrated Drive Electronics (IDE) interface for floppy disk and hard drives. Modern PCs may contain some of these interfaces, but there has been a steady transition to Universal Serial Bus (USB) and IEEE 1394 for peripherals, Peripheral Component Interconnect (PCI) bus for cards, and Enhanced IDE and AT Attachment (ATA) hard drives. Other specialized interfaces have been developed for various hardware and environments, such as Personal Computer Memory Card International Association (PCMCIA) devices for portable computers and Advanced Graphic Processor (AGP) bus interfaces for video cards.
With all of the advances in computer I/O standard, the underlying mechanics utilized by an operating system at boot-time to access these I/O devices has not changed that significantly. For example, x86 based PCs utilize a basic input/output system (BIOS) for startup functions such as self-test and providing a basic set of instructions used to boot the computer. On most current computer motherboards, the BIOS is stored in an Electrically Erasable Programmable Read-Only Memory (EEPROM,) also known as a “Flash” BIOS. Use of an EEPROM allows users to upgrade the BIOS when updates are made available.
The use of the BIOS has allowed a wide array of products to be usable at boot time by an operating system. The BIOS provides a standard layer of services that the operating system can use to “talk” to the hardware. The design of the BIOS has continually required modification due to some inherent limitations. For example, the addressing space that was defined for the system BIOS in earlier PC systems limited access to drives with a capacity of greater than 8.4 GB (7.9 GB on some systems.). These system BIOS of that era did not have adequate address locations to access more than 8.4 GB.
Although solutions were found for these problems, the “PC-AT” boot environment presents challenges to innovation in the computer industry. Advances in platform capabilities require hardware developers to adopt complex work-arounds, and require OS developers to make substantial changes to boot code. In response to this, the Extensible Firmware Interface (EFI) Specification was developed. The EFI defines an interface between the computer firmware and the operating system (OS). The EFI provides standard boot and run-time services to the OS that allows for platform innovation without requiring new boot-code be written for the OS.
Although EFI will provide an evolutionary path away from the legacy “PC-AT” boot environment, it will be appreciated that many currently used operating systems are still optimally configured to access lowest-common-denominator devices, most notably removable storage devices (e.g., floppy drives and CD-ROM). These devices may or may not be present at boot or run-time, but it is a safe assumption that an OS will have the capability to interact with these devices if they are present at boot time.